Castra Vetera
But for unknown reasons, this was not enough for the Batavians. Civilis chose to pursue vengeance and swore to destroy the two Roman legions. The timing was well chosen. With the civil war of the Year of the four emperors at its peak, it would take some time before Rome could produce an effective counterattack. Moreover, the eight Batavian auxiliary units of Vitellius' army were on their way home and could be easily persuaded to join the rebellion for an independent Batavia. This was an important reinforcement. Apart from being veteran troops, their numbers were greater than the combined Roman troops stationed in Moguntiacum (Mainz) and Bonna (Bonn).
In September 69, Civilis initiated the siege of Castra Vetera, the camp of the 5,000 legionaries of V Alaudae and XV Primigenia. The camp was very modern, filled with supplies and well defended, with walls of mud brick and wood, towers and a double ditch. After some failed attempts to take the camp by force, Civilis decided to starve the troops into surrender.
Meanwhile, Flaccus decided to wait for the result of the war in Italy. Not long before, the Rhine legions had been punished by Galba for their actions against the rebel Vindex of Gallia Lugdunensis. Vespasian was winning the war and Civilis was helping him to become emperor by preventing at least the two legions besieged in Xanten, loyal to Vitellius, from coming to his rescue. Flaccus and his commanders did not want to risk a second military gaffe and decided to wait for instructions.
But the news of Vitellius' defeat arrived and Civilis still continued the siege. He was not fighting for Vespasian; he was fighting for Batavia. Flaccus started to prepare a counterattack to rescue the besieged legions. Civilis was not going to wait until they were fully prepared and launched a surprise attack. In the evening of December 1 his best eight cavalry regiments attacked the Romans in Krefeld. The Roman army won the battle and destroyed the Batavian cavalry. But their own losses were enormous.
Knowing that the Romans would come to Castra Vetera, Civilis abandoned the siege and threatened to attack Moguntiacum. The Romans were misled and rushed to the rescue of their main base in Germania Superior. In Moguntiacum they received the news of Vespasian's accession to the throne. Flaccus decided to celebrate the event by distributing a sum of money to the legions. But these legions were historically loyal to Vitellius, their former commander, and this act of generosity was interpreted as an offense. Flaccus was murdered and his second-in-command deserted, leaving the Roman army in a state of confusion.
Civilis saw his chance and before the Romans knew what was happening, his troops besieged Castra Vetera once more.
Read more about this topic: Revolt Of The Batavi